Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently May Sun 31, 2020 2:00 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 24 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: HP 410B Repair
PostPosted: Apr Tue 07, 2020 6:46 pm 
Member

Joined: Jan Mon 20, 2014 6:21 pm
Posts: 115
Location: Texarkana, AR
I am working on a HP410B VTVM. The filter capacitor shorted and took out my 6X4 rectifier tube. I don't have a spare. Would it be
recommended to replace the tube with silicon diodes, of which I have plenty? Thanks for any opinions.
Wes
K5APL


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Tue 07, 2020 7:41 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 16624
Location: Albuquerque, NM 87123
No.


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 12:18 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 9476
Location: Long Island NY
You could stick a couple of diodes in there as a temporary expedient to see if the rest of the meter works, but leaving them in there permanently could prove regrettable. The 410B was designed and calibrated for a 6X4; with diodes you could get more power transformer heating due to higher peak currents in the HV winding, higher B+ voltages and the resulting need for extensive re-calibration, and maybe slamming the meter when the power is first turned on since the B+ voltage will come up instantly with diodes while the rest of the tubes still have to warm up.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 3:12 am 
Member
User avatar

Joined: Mar Sun 20, 2016 11:04 pm
Posts: 539
Location: Mesa, AZ 85206
I was thinking about the start of the issue...the filter capacitors shorting and taking out the 6X4...

Would it make sense to make sure the transformer is still OK before going too much farther?


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 3:38 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 3942
Location: Tucson, Arizona U.S.A.
I haven't heard of a shortage of 6X4s. It's always best to keep things the way they were designed unless there is a known problem that needs to be fixed.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 4:55 am 
Member
User avatar

Joined: May Mon 18, 2009 5:55 pm
Posts: 3007
Location: Erie, PA
I have heard of a few 410B power transformers taken out by shorted 6X4's, but this rectifier tube isn't ran hard at all in this application so it's rare. But it's a good idea to check the 300V transformer secondary voltages before moving forward. 6X4's are a $10-12 item all day, and as is the case with anything HP best to never change the circuit design unless there is no other option.

-Mark-


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 6:28 am 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3951
Location: Florida
I wouldn't be all that concerned about using diodes but I'd add resistance after them to get the voltage in the right region. I'd also check to see if the filament voltage went up to any significant degree without the 6X4 load.

Look for a 6X4 and none of this will matter. $5 at Radio Electric Supply.

RRM


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 7:14 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 4334
Location: Lincoln City, OR 97367
Greetings to the Forum:

I have a 410B with diodes bridged across the 6X4 socket. Been that way for years with no ill effects. I am skeptical of the peak current being hard on the transformer issue. Peak current is peak current... RMS current is something else. The peak currents may be higher, but the amount of ENERGY supplied by the transformer over time is the same. Divide by time and the RMS current will be the same for both rectifiers. The fact that the voltage will be a bit higher is the only reason to worry about the current; the additional heating effects (which is what will kill the transformer) are negligible.

True, the filter cap sees quite a bit of voltage until the tubes heat, but the one in my 410 seems to have survived OK thus far.

I don't believe that the B+ voltage will affect the meter calibration. The critical stage is regulated by an 0A2 and the meter driver amp is non-critical.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 11:47 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 9476
Location: Long Island NY
Quote:
I am skeptical of the peak current being hard on the transformer issue. Peak current is peak current... RMS current is something else


I think the answer is looking you right in the eye. If there's no difference, then what are all these dropping resistors for that everybody keeps installing? Replacing a tube rectifier with a silicon diode removes anywhere from 15 volts to as much as 50 volts of drop from the circuit. The current increases proportionally and you get more heating in the power transformer and everywhere else. Including the 0A2 voltage regulator tube which will change its voltage a few percent and maybe affect the calibration of the meter. If the meter was completely insensitive to B+ voltage changes, the 0A2 would have been superfluous.

If a dropping resistor is installed to get the voltages and currents back to where they were before, then the power that was dissipated in the plates of the tube rectifier is dissipated in the resistor. But even with a dropping resistor, a diode still has a much steeper transfer characteristic (more or less an on/off switch) than a tube rectifier, which can result in higher peak currents which the filter capacitors will try to deal with as higher ripple. I-squared-R still applies so there's incrementally more loss in the transformer windings and in the steel, if it is pushed closer to saturation.

The transformer in the 410-B was designed and tested for use with a 6X4. Had they planned on silicon diodes, HP probably would have made the transformer somewhat differently and tested it with diodes. So can you use silicon diodes in a 410-B? Yeah you probably can even if it's not everybody's first choice. Anecdotal evidence is that the differences are hardly noticeable. That's not true with all kinds of equipment, BTW, where plug-in silicon rectifier replacement "tubes" have done lots of damage. But my 410-B is still on the same 6X4 it had when it was given to me some 30 years ago so I don't really know what happens when you put silicon diodes in one and there is no hard data from HP on the subject. Therefore I would rather not suggest that somebody should go off and take chances with their meter.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Last edited by Chris108 on Apr Wed 08, 2020 1:05 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 12:40 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6909
Location: Sunbury, Ohio 43074
I would agree with keeping the 6X4 whether or not diodes work. If it ain't broke, don't fix it. As someone pointed out, there is not likely to be any shortage of 6X4 tubes. HP designed this for a tube, it works well with a tube, it's got other tubes..... so why try to eliminate the tube?

Pop a few diodes in temporarily if you are in a hurry, but any other work, such as calibration, will probably have to be redone once you get the new 6X4. Personally I'd set it aside till my bright shiny new $5 tube arrives. ;-)

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 10:45 pm 
Member

Joined: Jan Mon 20, 2014 6:21 pm
Posts: 115
Location: Texarkana, AR
I have a friend in town who gave me a 6X4 and I put it in the 410B. The closest capacitor I had to the original was a 10mFd at 450vdc so I put it in the circuit. The meter works now; DC Zero is good but AC Zero is at the end of the pot's travel and still not quite on the zero line. I need to do a Calibration and then see if it cures this problem.
BTW I had to replace V3 because after a few minutes the meter went full scale and stayed there. I did have a spare 12AU7 and it
seems to be working OK.
And, the 6X4 I removed from the meter was tested on my Precision tube tester. 1/2 had almost zero emission and it also had an internal short. Good thing I didn't put it back in the 410B.
So Calibration is next, and possibly seeing why the AC zero is skewed.
Thanks for all your comments.
BTW the audio folks apparently have driven the cost of the lowly 6X4 up to astronomical regions, especially on ebay.


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Wed 08, 2020 10:50 pm 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3951
Location: Florida
k5apl wrote:
...BTW the audio folks apparently have driven the cost of the lowly 6X4 up to astronomical regions, especially on ebay.


Forget eBay. Look at real tube sellers like Radio Electric Supply or ESRC: $5.

RRM


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 12:05 am 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6909
Location: Sunbury, Ohio 43074
Ebay sellers rarely get their listed price for such things. Check “sold” prices. Also I agree. Forget the bay for tubes

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 3:56 am 
Member

Joined: Jan Mon 20, 2014 6:21 pm
Posts: 115
Location: Texarkana, AR
I tried ESRC but could leave no message or contact info. Hope covid didn't get them.

I'll try other places and avoid ebay to buy tubes.


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 7:41 am 
Member

Joined: Nov Fri 30, 2012 3:35 am
Posts: 335
Location: Phoenix, AZ
(edit)
K5APL,
See my PM to you.
R/ John


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 11:30 am 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6909
Location: Sunbury, Ohio 43074
There are a bunch of tube sellers here on ARF as well .... you could always put a want ad in the classifieds

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 7:16 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 2178
Location: Dallas, TX
k5apl wrote:
I tried ESRC but could leave no message or contact info. Hope covid didn't get them.

I'll try other places and avoid ebay to buy tubes.

There is an order form.

Also
FindATube http://findatube.com/

Vacuum Tubes, Inc. https://vacuumtubesinc.com/

And if you have to ($$) Antique Electronic Supply https://www.tubesandmore.com/

Ebay for anything as a last resort. Years ago you could get a good deal, not anymore.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 7:33 pm 
Member

Joined: Jan Thu 24, 2019 1:22 pm
Posts: 246
Location: Centennial, Colorado 80122
I on't understand the fear in buying a tube on ebay if its misrepresented you can get your money back including the shipping. Some NOS listed with shipping for less than $10.


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 7:44 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6909
Location: Sunbury, Ohio 43074
I think in this case it was the cost, not any real fear....... not sure. I agree, Paypal covers the buyer. But it can be more of a hassle than dealing with one of the forum tube sellers for sure.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: HP 410B Repair
PostPosted: Apr Thu 09, 2020 7:53 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 9476
Location: Long Island NY
I'll second one of the sources mentioned above if you need it: http://findatube.com/

On their current price list, 6X4 is $4.50 new, $2.00 used/tested good. They guarantee their tubes. There was a point in time when nearly every car radio on the road had a 6X4 rectifier, plus they went into lots of AM/FM tuners, tape recorders, and other equipment. It's not a scarce tube.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
Post New Topic Post Reply  [ 24 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Don Cavey, steveh1155 and 12 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB